1. Field of the Invention
The present invention relates to wireless communication performing media access control on the basis of a carrier sense state, more specifically relates to a wireless communication apparatus and a wireless communication method for allowing a plurality of users to share and use a plurality of channels.
2. Description of the Related Art
Media access control (MAC) is control for determining how a plurality of communication apparatuses to make communication by sharing the same medium should use the medium to transmit communication data. By performing MAC, an event (a so-called collision) that a communication apparatus on reception side cannot separate the communication data is reduced even if two or more communication apparatuses simultaneously transmit the communication data by using the same medium. An event that a medium is not used by any communication apparatus is reduced by the MAC although a communication apparatus having a transmission request is present.
In wireless communication, it is hard for a communication apparatus to monitor transmission data while transmitting data, so that the MAC not based on collision detection is required. The IEEE 802.11 being a representative technology standard for wireless local area network (LAN) adapts carrier sense multiple access with collision avoidance (CSMA/CA).
CSMA/CA in IEEE 802.11 sets a period (referred to as duration) until a series of sequences composed of one or more frame exchanges succeeding from the corresponding MAC frame achieves the termination for a header of a MAC frame. A communication apparatus having no relation to the sequences and having no transmission right during the duration waits for transmission by determining a virtually occupied state of a medium. Thereby, occurrence of the collision is avoided. In contrast, a communication apparatus having no transmission right in the sequences recognizes that the medium is not used other than the period with the medium is actually occupied therein.
IEEE 802.11 defines that a combination of a virtual carrier sense of a MAC layer like the former and a physical carrier sense of a physical layer like the latter determines a state of the medium and the MAC is performed on the basis of the resulting determination.
Jpn. Pat. Appln. KOKAI Publication No. 2003-87856 discloses a method for achieving a wireless base station sharable by a plurality of wireless LAN systems in a wireless communication system with a plurality of wireless LAN systems different in physical layers coexisted therein. Specifically, the shared wireless base station generates a first notification signal of a first physical layer and a second notification signal of a second physical layer one after another to transmit them to a wireless terminal and switches between the first and the second physical layers in synchronous with the first and the second notification signals. A wireless terminal corresponding to the first physical layer can access only for a specified time from a time of transmission of the first notification signal and a wireless terminal corresponding to the second physical layer can access only for a specified time from a time of transmission of the second notification signal.
IEEE 802.11 conventionally adopting the CSMA/CA has been achieving a high communication speed by mainly changing protocol in a physical layer. With respect to the 2.4-GHz band, IEEE 802.11 (established in 1997, communication speed=2 Mbps) has changed to IEEE 802.11b (established in 1999, communication speed=11 Mbps) and, moreover, has changed to IEEE 802.11g (established in 2003, communication speed=54 MHz). With regard to 5-GHz band, only IEEE 802.11a (established in 1999, communication speed=54 MHz) currently exists as a standard specification.
There exists a method for expanding the bandwidth of a channel as one for approaching a high communication speed. Jpn. Pat. Appln. KOKAI Publication No. 2003-06323 conventionally presented a communication system for performing MAC to different channels coexisting within the same frequency band in the case that the frequency band of the channel is expanded.
Jpn. Pat. Appln. KOKAI Publication No. 2003-06323 describes the communication system which achieves broadband communication with a plurality of channels used simultaneously therein by MAC to make a reservation for a plurality of channels one by one in order. However, since a control frame to reserve a channel for broadband communication is also transmitted in accordance with the same channel access procedures as those of other control frame and other data frame, the described communication system cannot assure a channel for the broadband communication without having to win a competition. That is, the conventional communication system cannot always surely start the broadband communication. Therefore, it is necessary for a secured start of the broadband communication to give a channel access right with a high priority to the control frame to reserve a plurality of channels for the broadband communication.
A system for performing channel access according to parameters due to priority class has already proposed, in which the system gives a priority class to data frame in response to a kind of data as IEEE 802.11e of a wireless LAN specification gives to the data frame. Also with respect to a control frame, a system for setting a priority class corresponding to a type of the following data frame to the control frame has already proposed. For example, at the time of transmission of an RTS/CTS frame, the proposed system performs channel access in accordance with a parameter of a priority class corresponding to the type of the following data.
However, a system for performing channel access by setting a priority class to a control frame itself independently of the kind of the following data frame has not presented yet. Especially, it is not proposed that the determination whether a priority of channel access should be given or not to the control frame on the basis of the fact whether or not a control frame for a channel reservation for the broadband communication.
Jpn. Pat. Appln. KOKAI Publication No. 2003-06323 does not take into account at all a time required to switch a channel or a communication bandwidth caused at the time of channel access to a different frequency band. Accordingly, the system disclosed by Jpn. Pat. Appln. KOKAI Publication No. 2003-06323 degrades use efficiency of a channel if it takes a long time to switch the channel or the communication bandwidth.
When the system described above makes communication among terminals differing switching times of the channel or the communication band from one another, if a source terminal has no information about the switching time of the channel or the communication bandwidth at a destination terminal, a frame is occasionally transmitted before completion of switching of the channel or communication bandwidth at the destination terminal.